In an aromatic alkylation process, alkylated aromatic compounds are prepared by alkylating an aromatic compound with an alkylating agent. The alkylation process is typically carried out in the presence of an acid which can be in the form of either a liquid or a solid. Examples of such acids include AlCl.sub.3, BF.sub.3, and zeolites. Zeolites are preferred in many instances because they eliminate problems associated with disposal and reclamation. The particular alkylated aromatic product that is desired is often a monoalkylated aromatic compound such as ethylbenzene or cumene (isopropyl benzene). Polyalkylated aromatic compounds may be formed in the process of manufacturing the monoalkylated product, and must be either removed or converted. Advantageously, there are transalkylation reactions that convert the polyalkylated aromatic to the desired monoalkylated aromatic compound. For example, in a process scheme to produce ethylbenzene, unwanted diethylbenzene produced in the alkylation step is converted to ethylbenzene in a transalkylation step. Thus, a transalkylation step is often an integrated part of a high yield alkylation process.
The polyalkylated aromatic feedstream to the transalkylation reactor may contain impurities such as aromatic or aliphatic olefins, aromatic or aliphatic diolefins, styrene, oxygenated organic compounds, sulfur containing compounds, nitrogen containing compounds such as collidine, oligomeric compounds such as polystyrene, and combinations thereof. Whereas vapor phase transalkylation processes are typically resistant to the presence of such impurities, liquid phase transalkylation processes are very susceptible to catalyst contamination, deactivation, plugging and the like by virtue of contact with any or all of these transalkylation feed contaminants. Many other factors favor liquid phase transalkylation units in an overall alkylation process scheme, and therefore a method and apparatus to effectively remove such contamination would be desirable.
Many methods and materials have been proposed for the removal of contaminants from hydrocarbon streams. U.S. Pat. No. 2,778,863 describes a multi-step clay treatment process for aromatics containing streams to overcome the clay fouling problems caused by diolefins in other clay treatment processes. Clays such as bentonite or synthetic alumina and/or silica-containing material are disclosed in U.S. Pat. No. 3,835,037 for use in a low temperature process for oligomerization/polymerization of color forming olefinic impurities in an aromatics stream such as a naphtha fraction. A process utilizing a silica alumina cracking catalyst in slurry form to contact and polymerize olefins and diolefins in a steam cracked naphtha stream is proposed in U.S. Pat. No. 3,400,169. The proponents of the process disclosed in U.S. Pat. No. 4,795,550 surveyed the aforementioned hydrocarbon purification processes and proposed the use a liquid phase process with a solid medium comprising a crystalline aluminosilicate zeolite such as faujasite and a refractory oxide to remove bromine-reactive olefinic impurities from aromatics containing streams. Co-pending, commonly assigned U.S. patent application Ser. No. 09/017,777, entitled "DECREASING BI REACTIVE CONTAMINANTS IN AROMATIC STREAMS", discloses a process wherein the aromatics stream is pre-treated to remove di-olefins prior to contact with the acid active catalyst material which removes mono-olefinic bromine reactive hydrocarbon contaminants.
Hydrocarbon separation processes utilizing the selective sorption properties of certain zeolite materials, including specially treated zeolite materials, have been proposed in U.S. Pat. Nos. 3,888,939 and 4,309,281. The removal of nitrogen containing compounds from a hydrocarbon stream by using a selective adsorbent, such as ZSM-5, having an average pore size less than about 5.5 Angstroms is disclosed in U.S. Pat. Nos. 5,744,686, 5,330,946 discloses a bentonite clay-based catalyst, suitable for removing olefins from aromatics streams, manufactured by adhering together a plurality of smaller acid-activated bentonite clay particles using a strong mineral acid as a binder. The use of spent catalysts for purification of aromatic streams by diolefin saturation and CCR removal at temperature low enough to reduce olefin polymerization reactions is proposed in U.S. Pat. No. 4,501,652.
It would be desirable to have a simple, single step process suitable for removing and/or converting most or all of the various different types of organic and inorganic contaminants which may be present in an alkylation/transalkylation process unit such that the valuable liquid phase transalkylation catalyst material will not be deactivated and/or plugged by these contaminants, thus reducing downtime and capital costs, while improving yields and material costs.